Electric power transmission device and electric power transmission system

ABSTRACT

One aspect of the present invention is an electric power transmission device that periodically shifts a frequency of a magnetic field to a plurality of predetermined shift values and that transmits electric power by utilizing the magnetic field. The device includes a plurality of power transmitters and an instructor. Each of the plurality of power transmitters configured to generate a magnetic field. The instructor outputs an instruction signal indicating a shift value to be shifted to each of the power transmitters to instruct the shift value to be shifted to each of the power transmitters. Further, the instructor instructs the shift value to be shifted in such a manner that at least a part of the magnetic fields of the plurality of power transmitters are different in frequency at the same time point.

CROSS-REFERENCE TO RELATED APPLICATION (S)

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-132587, filed Jul. 12, 2018; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electric powertransmission device and an electric power transmission system.

BACKGROUND

Contactless power transmission (contactless power supply) from anelectric power transmission device to an electric power reception deviceis becoming popularized. In the contactless power supply, a powertransmission circuit generates high-frequency current of a predeterminedfrequency, the high-frequency current excites a power transmission coil,and a magnetic field generated by the excitation transmits electricpower. In the contactless power supply, however, there is concern that amagnetic field leaked to the outside (leakage electromagnetic field) mayinterfere with broadcasting, wireless communication, and the like.Therefore, the contactless power supply is required to suppress theleakage electromagnetic field so as to satisfy restrictions relating tothe upper limit of the leakage electromagnetic field determined byinternational standards and the like.

One of techniques capable of suppressing the leakage electromagneticfield is frequency hopping. Frequency hopping is a technique forperiodically causing the power transmission frequency to shift so as tospread and reduce the leakage electromagnetic field. However, when thefrequency hopping is performed, the output current from the electricpower reception device may become pulsating current larger in rippledepending on frequency characteristics. Therefore, there is a risk thata battery or the like may fail when receiving the output current. Inorder to prevent this, it is necessary to control input power andcorrect frequency characteristics of the electric power transmissiondevice and the electric power reception device. However, it is difficultto accurately grasp changing frequency characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of an electric powertransmission system according to a first embodiment.

FIGS. 2A and 2B are diagrams illustrating an exemplary frequencyhopping.

FIG. 3 is a diagram illustrating an example of time sequential frequencyshifting.

FIG. 4 is a diagram illustrating an exemplary configuration of aninverter.

FIGS. 5A to 5D are diagrams illustrating a first example of thepositional relationship between shift value range and amplitude ratio.

FIG. 6 is a diagram illustrating frequency shifting in lines A and B.

FIGS. 7A to 7C are diagrams illustrating differences in amplitude ratiowhen the shifting phase difference is kept at 360/M in the firstexample.

FIGS. 8A to 8C are diagrams illustrating another example of thefrequency shifting.

FIGS. 9A to 9D are diagrams illustrating a second example of thepositional relationship between shift value range and amplitude ratio.

FIGS. 10A and 10B are diagrams illustrating differences in amplituderatio when the shifting phase difference is kept at 180/M in the secondexample.

FIG. 11 is a diagram illustrating a modified example of the firstembodiment.

FIG. 12 is a block diagram illustrating an example of an electric powertransmission system according to a second embodiment.

FIG. 13 is a diagram illustrating processing relating to deletion of acombination of shift values of respective lines at each time point.

FIGS. 14A and 14B are diagrams illustrating an exemplary shifting in thecase of differentiating shift values for each line.

FIGS. 15A and 15B are diagrams illustrating another exemplary shiftingin the case of differentiating shift values for each line.

FIG. 16 is a diagram illustrating an exemplary arrangement of powerreception coil units.

FIG. 17 is a diagram illustrating an exemplary arrangement of powerreception coil units that are a solenoid type.

FIG. 18 is a diagram illustrating an exemplary arrangement of powerreception coil units utilizing the reversed phase.

FIG. 19 is a diagram illustrating an exemplary arrangement of powerreception coil units utilizing the reversed phase when the powerreception coil units use coils of the solenoid type.

DETAILED DESCRIPTION

An embodiment of the present invention provides an apparatus capable ofreducing the ripple in the output current of a power reception device,in a contactless electric power transmission system including aplurality of electric power transmission lines, without graspingfrequency characteristics in advance.

One aspect of the present invention is an electric power transmissiondevice that periodically shifts a frequency of a magnetic field to aplurality of predetermined shift values and that transmits electricpower by utilizing the magnetic field. The device includes a pluralityof power transmitters and an instructor. Each of the plurality of powertransmitters configured to generate a magnetic field. The instructoroutputs an instruction signal indicating a shift value to be shifted toeach of the power transmitters to instruct the shift value to be shiftedto each of the power transmitters. Further, the instructor instructs theshift value to be shifted in such a manner that at least a part of themagnetic fields of the plurality of power transmitters are different infrequency at the same time point.

Below, a description is given of embodiments of the present inventionwith reference to the drawings. The present invention is not limited tothe embodiments. In the drawings, each alphabet suffixed to a referencenumeral is attached for distinguishing each individual denoted by thesame reference numeral.

First Embodiment

FIG. 1 is a block diagram illustrating an exemplary electric powertransmission system according to a first embodiment. The electric powertransmission system according to the first embodiment includes anelectric power transmission device 1 and an electric power receptiondevice 2. The electric power transmission device 1 transmits electricpower by utilizing magnetic field. The electric power reception device 2receives the transmitted electric power.

The electric power transmission device 1 includes an AC power source 11,an AC-DC converter 12, a plurality of power transmitters 13, and a drivesignal generator (instructor) 14. Each power transmitter 13 includes aninverter 131 and a power transmission coil unit (resonator) 132. Theelectric power reception device 2 includes a plurality of powerreceptors 21 and an adder 22. Each power receptor 21 includes a powerreception coil unit (resonator) 211 and a rectifier 212.

The electric power transmission system according to the presentembodiment transmits electric power from the electric power transmissiondevice 1 to the electric power reception device 2 by utilizing magneticfield generated from high-frequency current due to electromagneticinduction. That is, the electric power transmission system according tothe present embodiment can realize contactless power supply to theelectric power reception device 2.

Further, in the present embodiment, a plurality of electric powertransmission lines is provided. That is, electric power, namely, aplurality of high-frequency currents, is transmitted from the electricpower transmission device 1 to the electric power reception device 2 byutilizing a plurality of magnetic fields. It is assumed that the adder22 sums up the plurality of high-frequency currents received by theelectric power reception device and outputs the summed-up current.

In the following description, each electric power transmission line issimply referred to as a line. In FIG. 1, a first power transmitter 13Aand a first power reception coil unit 211A cooperatively configure aline A. Similarly, a second power transmitter 13B and a second powerreception coil unit 211B cooperatively configure a line B. However, theelectric power transmission system may be configured to include three ormore lines. In FIG. 1, as indicated by a dotted frame, another linedifferent from the line A and the line B may be provided additionally.It is needless to say that the lines in the electric power transmissionsystem may be limited to only two of the line A and the line B.

The magnetic field generated by the electric power transmission device 1of a contactless power supply system is not only used for electric powertransmission to the electric power reception device 2 but also partlyinfluences as a leakage electromagnetic field that interferes withperipheral devices. Therefore, the electric power transmission systemaccording to the present embodiment performs frequency hopping forspreading electric power energy to a predetermined bandwidth (spreadbandwidth) on the frequency axis.

For example, the electric power transmission system shifts the switchingfrequency when generating high-frequency current that generates themagnetic field, thereby causing the frequency of the high-frequencycurrent to shift. It is known that the frequency of the magnetic fieldband is spread thereby and the intensity thereof decreases compared to acase where no shifting occurs in the frequency of the high-frequencycurrent. That is, the frequency hopping is to cause the frequency of themagnetic field, namely the frequency of the high-frequency current, toshift. The frequency hopping can suppress the intensity of the leakageelectromagnetic field.

FIGS. 2A and 2B are diagrams illustrating an exemplary frequencyhopping. FIG. 2A is a diagram illustrating a relationship betweenfrequency and magnetic field intensity in the case of not performing thefrequency hopping, that is, when performing electric power transmissionat only one frequency. According to the example illustrated in FIG. 2A,the electric power transmission is performed only at 85 kHz. Therefore,the illustrated graph has one peak (local maximum point) at the point of85 kHz.

FIG. 2B is a diagram illustrating a relationship between frequency andmagnetic field intensity in the case of performing the frequencyhopping, that is, when performing electric power transmission at aplurality of frequencies. According to the example illustrated in FIG.2B, the electric power transmission is performed at 20 frequenciescentered on 85 kHz. Therefore, the illustrated graph has 20 peaks. Inparticular, the smallest frequency Fss_START (f₁) is set to 81.2 kHz,the interval between frequencies to be used is set to 400 Hz, and thenumber of frequencies is 20. Accordingly, the highest frequency Fss_END(f20) is set to 88.8 kHz.

Hereinafter, the value to which the frequency shifts when performing thefrequency hopping is simply referred to as a shift value. Further, it isassumed that respective shift values are numbered in order from thesmaller one, and i-th (i is an integer equal to or greater than 1) shiftvalue is expressed as f_(i). That is, a first shift value f₁ is theminimum shift value (minimum frequency), a shift value f_(i) is the i-thlargest shift value, and f_(i+1)>f_(i) is satisfied. Further, the numberof shift values is referred to as a shifting number. According to theexample illustrated in FIG. 2B, the shifting number is 20.

In the frequency hopping, at certain timing, the frequency shifts fromone of the shift values to another of them. Performing such shiftingmany times can spread the frequency and lower the intensity of theleakage electromagnetic field. The frequency difference (f_(i+1)−f_(j))between neighboring shift values is referred to as a shifting width. Inthe following description, it is assumed that the frequency hopping isshifting to a neighboring shift value.

In the long view, the electric power in the case of performing suchfrequency hopping is the same as electric power in the case of notperforming the frequency hopping. Therefore, the electric power perfrequency (power density) when the frequency hopping is performed issmaller than that in the case of not performing the frequency hopping.The average power amount in a long period decreases as a function of1/Bss, Bss representing the spread bandwidth. In this manner, byperforming the frequency hopping, the electric power energy can bespread at a plurality of frequencies and the power density measured asthe leakage electromagnetic field can be reduced. The effect of loweringthe leakage electromagnetic field by the frequency hopping is referredto as a frequency spreading effect.

The spread bandwidth may be set to be greater than the interval betweenthe minimum frequency and the maximum frequency. In other words, in thecase of determining the spread bandwidth in advance, the maximumfrequency and the minimum frequency may be determined in such a mannerthat the interval between the maximum frequency and the minimumfrequency becomes smaller than the spread bandwidth. This is because, ifthe interval between the maximum frequency and the minimum frequency isequalized with the spread bandwidth, it may exceed the spread bandwidthdue to the spread of the frequency when performing the frequencyhopping. According to the example illustrated in FIG. 2B, by definingthe spread bandwidth as the number of frequencies×the shifting width andsetting the spread bandwidth to be 8 kHz (20×400 Hz), it is set to belarger than the interval between the maximum frequency and the minimumfrequency (Fss_END−Fss_START=7.6 kHz). That is, a half bandwidth of theshifting width is given as a buffer to both ends of the band between themaximum frequency and the minimum frequency.

FIG. 3 is a diagram illustrating an example of time sequential frequencyshifting. In FIG. 3, the horizontal axis represents the time and thevertical axis represents the number of the shift value. FIG. 3illustrates an exemplary frequency shifting in the case of repeating theshifting based on a predetermined rule using 20 shift values from f₁ tof₂₀ illustrated in FIG. 2B. The predetermined rule is, for example, tocause the shift value to shift from the minimum value f₁ in ascendingorder, and after reaching the maximum value f₂₀, cause the shift valueto shift in descending order to return to the minimum value Causing thefrequency of the magnetic field to periodically shift to a plurality ofshift values as illustrated in FIG. 3 can stably obtain the frequencyspreading effect. That is, in order to realize a periodic shifting ofthe frequency, it is preferred to perform control in such a manner thatthe shifting to the same shift value occurs repeatedly at constantintervals.

When k is defined as an integer greater than 1, one cycle in theperiodic shifting illustrated in FIG. 3 is from a time point when thefrequency shifts from the shift value f_(k+1) or f_(k−1) to the shiftvalue f_(k) to a subsequent time point when the frequency shifts againfrom the same shift value f_(k+1) or f_(k−1) to the shift value f_(k).The one cycle is, for example, from the time point when the frequencyshifts from the shift value f₁₁ to the shift value f₁₂ to the subsequenttime point when the frequency shifts again from the shift value f₁₁ tothe shift value f₁₂.

In the present embodiment, the shift value at the start of frequencyhopping, namely an initial value, varies depending on the line. Further,the order of shifting is also variable depending on the line. Thefrequency sustaining time is assumed to be the same in each line, but itmay be differentiate for each shift value. For example, in FIG. 3, thesustaining times of the shift values and f₂₀ are doubled. Whenoutputting a drive signal for causing the frequency to shift to theshift value f₁ or f₂₀, this may be realized by outputting a drive signalfor causing the frequency to shift to the same shift value f₁ or f₂₀again at the next timing for adjusting the drive signal.

As illustrated in FIG. 3, since the frequency first shifts in ascendingorder or in descending order and then shifts oppositely, the shape ofthe shifting on the graph is triangular. Therefore, such a shiftingstate is referred to as a “triangular wave shift”.

In the present embodiment, frequency spreading can be obtained throughsuch frequency hopping, that is, by causing the frequency of thehigh-frequency current to sequentially shift at constant time intervals,simultaneously in respective lines. However, in the case of providing aplurality of lines as in the present embodiment, if the frequencyhopping is performed without any control in each line, the outputcurrent from the electric power reception device 2 to be generated bycombining the high-frequency currents of respective lines may become apulsating current larger in ripple.

In general, the contactless power supply system has amplitudecharacteristics in which the amplitude differs for each frequency.Therefore, the output power to be obtained in each frequency whenperforming the frequency hopping varies depending on the frequencyamplitude characteristics. It causes that the high-frequency current ineach line increases and decreases with shifting of the frequency and itswaveform undulates. If high-frequency currents having large amplitudeare combined, the combined amplitude further increases and the outputcurrent will become a pulsating current larger in ripple. Therefore, inthe present embodiment, by adjusting the order of frequency shifting foreach line, the ripple of the output current from the electric powerreception device 2 is reduced. Details of an adjustment method will bedescribed below together with constituent components.

An internal configuration of the electric power transmission device 1 isdescribed below.

The AC power source 11 supplies AC current to the AC-DC converter 12.The AC power source 11 may be a three-phase power source or asingle-phase power source. In addition, a power-factor improvingcircuit, a rectifier, and the like may be connected to the AC powersource 11.

The AC-DC converter 12 converts the supplied AC current into DC current.Then, the DC current from the AC-DC converter 12 is transmitted to eachpower transmitter 13. The AC-DC converter 12 may be configured to adjustthe amount of power transmission so as to control the voltage and thecurrent of electric power to be supplied to the power transmitter 13.That is, the AC-DC converter 12 may step up or down the input voltage ofthe inverter 131 (namely, the output voltage of the AC-DC converter 12)to a preferred voltage value.

Each power transmitter 13 generates a magnetic field of the frequencybased on the drive signal from the drive signal generator 14, by usingthe DC current from the AC-DC converter 12. The inverter 131 in thepower transmitter 13 generates high-frequency current from the DCcurrent supplied from the AC-DC converter 12. In particular, theinverter 131 includes a plurality of switching elements (hereinafter,referred to as switches) as constituent components, and each switchperforms switching so as to convert the input DC current into AC current(high-frequency current) of a preferred frequency at instructed timing.The timing of conversion is based on the drive signal (switching signal)from the drive signal generator 14. That is, high-frequency currentgeneration and the frequency hopping are performed based on the drivesignal. Then, the high-frequency current flows and it causes that thepower transmission coil unit 132 in the power transmitter 13 generates amagnetic field of the same frequency.

FIG. 4 is a diagram illustrating an exemplary configuration of theinverter 131 in the power transmitter 13. According to the exampleillustrated in FIG. 4, a switch A1 and a switch A2 are connected inseries so as to configure a leg A with the switch A1 as an upper arm andthe switch A2 as a lower arm. Further, a switch B1 and a switch B2 areconnected in series so as to configure a leg B with the switch B1 as anupper arm and the switch B2 as a lower arm. Further, the leg A and theleg B are connected in parallel. A connection node between the switch A1and the switch A2 is connected to one end of the power transmission coilunit 132. A connection node between the switch B1 and the switch B2 isconnected to the other end of the power transmission coil unit 132.Further, DC current is input to one end of the switch A1, which is notconnected to the switch A2, and to one end of the switch B1, which isnot connected to the switch B2. As a result, high-frequency current isgenerated from the DC current of the AC-DC converter 12 and flows intothe power transmission coil unit 132.

When the magnetic field generated by the power transmission coil unit132 reaches the power reception coil unit 211, mutual coupling occursbetween the power transmission coil unit 132 and the power receptioncoil unit 211. As a result, the power reception coil unit 211 canreceive electric power from the power transmission coil unit 132. Inthis manner, the electric power can be transmitted contactlessly. Thetype of the coil in the power transmission coil unit 132 may be either asolenoid type or a spiral type.

The power transmission coil unit 132 may include only the coil or mayadditionally include a capacitor. When connected between the coil andthe inverter 131, the capacitor operates as a compensation circuit. Thatis, the capacitor compensates the high-frequency current for thepurposes of: improving the power-factor before the high-frequencycurrent is transmitted to the coil; reducing the phase differencebetween the current and the voltage; and the like. The capacitor and thecoil may be connected in series or may be connected in parallel.

The drive signal generator 14 generates the above-mentioned drivesignal. By the generated drive signal, more specifically, by thefrequency of the drive signal changing to a value corresponding to theinstructed shift value, the frequency of the magnetic field generated bythe power transmitter 13 finally shifts to the frequency based on thedrive signal. Therefore, the drive signal can be said as an instructionsignal indicating a shift value to be shifted. Further, the drive signalgenerator 14 can be said as an instructor that instructs a shift valueto be shifted to each power transmitter 13. In the followingdescription, when the drive signal generator 14 is described asinstructing the shift value, it means that the drive signal generator 14outputs the drive signal indicating the shift value to be shifted.

The drive signal is given as a rectangular wave to each switch. Therectangular wave can be generated based on a predetermined setting valuesuch as a duty ratio, a dead time, or the like. The frequency of therectangular wave is shifted sequentially and it causes that thefrequency of the magnetic field for power transmission is shifted.

The timing of the frequency shifting can be instructed by dividing aclock signal and generating the drive signal based on the divided clocksignal. The settings, such as the shift values; the order according towhich the shift values are instructed; and the time interval of shifting(the period during which the frequency is sustained), are assumed to beregistered in advance in the drive signal generator 14. That is, thedrive signal generator 14 selects one shift value from a plurality ofshift values determined beforehand based on a predetermined rule andoutputs a drive signal adjusted so as to instruct the selected shiftvalue. This rule, according to which the shift value to be instructedfor each line is determined, varies depending on the positionalrelationship between shift value existing range and amplitude ratio.Therefore, how to instruct the shift value is explained below togetherwith some examples concerning this positional relationship. In thefollowing description, for simplification, the explanation will be madewith a smaller number of shifts. However, it is unnecessary to changethe actual shifting number.

(First Example of the First Embodiment, in which the Frequency Relatedto the Peak of Amplitude Characteristics is not Present in the Range ofShift Values)

FIGS. 5A to 5D are diagrams illustrating a first example of thepositional relationship between shift value range and amplitude ratio.In the first example, the peak of the amplitude ratio does not exist inthe shift value range. FIG. 5A is a diagram illustrating amplitudecharacteristics in the first example. FIG. 5B is an enlarged view ofFIG. 5A in a range where the frequency shifting is performed. FIGS. 5Cand 5D are diagrams illustrating the order of shifting in the line A andthe line B. In FIG. 5A, the shift value range is on the right side ofthe peak of the amplitude ratio (that is, the minimum value of the shiftvalue is greater than the frequency related to the peak of the amplituderatio), although the shift value range may be on the left side of thepeak of the amplitude ratio (that is, the maximum value of the shiftvalue is smaller than the frequency related to the peak of the amplituderatio).

The amplitude characteristics mean a relationship (graph) betweenfrequency and amplitude ratio. The amplitude ratio represents a ratio ofthe electric power (or current) input from the electric powertransmission device 1 to the inverter 131 to the electric power (orcurrent) output from the adder 22 of the electric power reception device2. That is, the graph of FIG. 5A illustrates a change in the electricpower received by the electric power reception device 2 due to thefrequency shifting in the case where the input to the inverter 131 isconstant.

Although the amplitude characteristics are variable depending onconstant values, characteristics, and positional relationships ofconstituent components, such as inverters, rectifiers, capacitors, coilsand the like, it is assumed in the present embodiment that the electricpower transmission device 1 and the electric power reception device 2are designed so as to obtain preferred amplitude characteristicsconsidering component irregularities, manufacturing errors, and thelike.

In FIG. 5B, the shift values f₁ to f₅ are illustrated. In FIGS. 5C and5D, the shifting orders of shift values, namely, shifting patterns, inrespective lines are indicated by arrows. In the line A, first thefrequency shifts sequentially from f₁ to f₅ (as indicated by arrow 1 inFIG. 5C), subsequently shifts sequentially from f₅ to f₁ (as indicatedby arrow 2 in FIG. 5C), and again shifts sequentially from f_(i) to f₅(as indicated by arrow 3 in FIG. 5C). In the line B, the frequencyshifts sequentially from f₅ to f₁ (as indicated by arrow 1 in FIG. 5D),subsequently shifts sequentially from f₁ to f₅ (indicated by arrow 2 inFIG. 5D), and again shifts sequentially from f₅ to f_(i) (as indicatedby arrow 3 in FIG. 5D). The timing of shifting is the same for the lineA and the line B. Thereby, the sum of shift values of the lines A and Bis equalized.

FIG. 6 is a diagram illustrating frequency shifting in the lines A andB. Shift values f_(i) at each time point (the time point i) in the lineA and the line B are shown in the table. According to the exampleillustrated in FIG. 6, the shift value at the first time point, namely,the initial value, is set to f₁, and the shifting is repeated in such amanner that the shift value shifts from the initial value f₁ inascending order and after reaching the maximum value f₅, shifts indescending order and returns to the initial value f₁.

Further, the table in FIG. 6 includes shifting phases (phase angles)expressing respective shift values in the form of phase (angle). Theshifting phase expresses each shift value in the form of phase (phaseangle) by regarding one cycle of the periodic shifting as 360°, the onecycle including an ascending shift from the minimum value of shiftvalues to the maximum value and a descending shift from the maximumvalue to the minimum value. Therefore, the shifting phase correspondingto the initial shift value f₁ is 0°. The shifting phase corresponding tothe maximum shift value f₅ is 180°. The shifting phase when returning tothe initial value for the first time is 360°. Further, the shiftingphase when the shifting is repeated and returns to the initial valueagain is 720°. Therefore, when “p” is defined as an integer equal to orgreater than 0, if θ represents the shifting phase, θ=θ+360×p issatisfied.

Further, the shifting phase also indicates the direction of shifting. Itmeans that the shifting in a range of 0+360×p 9<180+360×p occurs inascending order and that the shifting in a range of 180×p<9<360×p occursin descending order. Accordingly, the shifting phase represents not onlythe shift value but also the shifting direction indicating whether theshifting occurs in ascending order or in descending order.

When instructing the shifting illustrated in FIGS. 5C and 5D, the drivesignal generator 14 instructs the shift value f₁ for the line A and theshift value f₅ for the line B, as initial values that are mutuallydifferent. Then, after instructing each initial value, the drive signalgenerator 14 instructs a shift value identical to that instructed lasttime or a shift value corresponding to a phase angle that is larger byone than the phase angle corresponding to the shift value instructedlast time. Thereby, the phase difference of the initial values isconstantly held as the shifting phase difference between the line A andthe line B. Therefore, when the minimum shift value and the maximumshift value are instructed as the initial values of the line A and theline B, the sum of shift values of the lines A and B can be equalized.

When the electric power transmission system includes M (M is an integerequal to or greater than 2) lines, it is preferred that the shiftingphase difference between respective lines be kept at 360/M°. In theabove-mentioned example including only two lines of the line A and theline B, the preferred shifting phase difference is 180° because M=2. Inthis case, the drive signal generator 14 can instruct, as the initialvalues, different shift values for realizing the shifting phasedifference of 360/M°. In this manner, when the shifting phase differencebetween respective lines is kept at 360/M°, fluctuations in the electricpower received by the electric power reception device 2 can be reduced.it is assumed that, as matter of course, the shifting phases ofrespective lines are not made the same. For example, when the totalnumber of lines is three, it is assumed that the shifting phase of theline A is set to 0°, the shifting phase of the line B is set to 120°,and the shifting phase of the line C is set to 240°. Although theshifting phase difference of the line B becomes 120°, the shifting phaseof the line C is not set to 0°. That is, it can be said that thedifference between phase angles corresponding to any two of the shiftvalues of power transmitters at the same time point is preferablycoincident substantially with any one of multiples from 1 to M−1 for360/M. In other words, when “m” is defined as an integer equal to orgreater than 1 and less than M, it is preferred that the differencebetween the phase angles be expressed by 360(M−m)/M.

Although the shifting phase is used to express the shifting pattern ofshift values in the above description, it is actually sufficient for thedrive signal generator 14 to register the table illustrated in FIG. 6,in which the order of shifting is indicated together with correspondingshift values.

The electric power received by the electric power reception device 2becomes a sum of transmission powers of respective lines added by theadder 22. Therefore, in the case of not adjusting the shifting phasedifference, there is a considerable difference in amplitude ratiobetween when the frequencies of the lines A and B are f₁ and when thefrequencies of the lines A and B are f₄. That is, large ripples occur.However, in the case of equalizing the sum of shift values of respectivelines, the composite amplitude ratio does not fluctuate so much.Therefore, no large ripple occurs.

FIGS. 7A to 7C are diagrams illustrating differences in amplitude ratiowhen the shifting phase difference is kept at 360/M in the firstexample. FIG. 7A illustrates amplitude characteristics in the case ofincluding two lines. FIG. 7B illustrates amplitude characteristics inthe case of including three lines. FIG. 7C illustrates amplitudecharacteristics in the case of including four lines. Each solid linegraph indicates amplitude characteristics when the shifting phasedifference between respective lines is adjusted to 360/M. In the case ofthree lines, the shifting phases of the line A, the line B, and thethird line are 0°, 120°, and 240°, respectively. In the case of fourlines, the shifting phases of the line A, the line B, the third line,and the fourth line are 0°, 90°, 180°, and 270°, respectively. Eachdotted line graph indicates comparable amplitude characteristics in thecase of in-phase, that is, when the shifting occurs at the samefrequency. The frequency on the horizontal axis of the graph indicatesthe frequency of the line A.

As illustrated in FIGS. 7A to 7C, regardless of the number of lines, thedifference between the maximum amplitude ratio and the minimum amplituderatio at the time of shifting phase adjustment is smaller than thedifference between the maximum amplitude ratio and the minimum amplituderatio in the case of in-phase. Accordingly, regardless of the number oflines, it is understood that adjusting the shifting phase can suppressthe difference between the maximum amplitude ratio and the minimumamplitude ratio to be smaller than the case of not adjusting theshifting phase.

Since fluctuations in the amplitude ratio can be minimized, it ispreferred to set the shifting phase difference to 360/M°. However, itmay be sufficient to avoid the case of in-phase where the differencebetween the maximum amplitude ratio and the minimum amplitude ratio ismaximized. That is, it may be sufficient to adjust in such a manner thatthe shifting phases of respective lines are different from each other atthe same time point, in other words, so that the frequencies of themagnetic fields generated by the plurality of power transmitters 13 aredifferent from each other.

The order of shifting in the above description is the triangular waveshifting as illustrated in FIGS. 5A to 5D and 6, in which the frequencyfirst shifts in ascending order or in descending order and then shiftsin the opposite direction. However, the order of shifting is not limitedto the triangular wave shifting.

FIGS. 8A to 8C are diagrams illustrating another examples of thefrequency shifting. As illustrated in FIG. 8A, in the line A, thefrequency shifts in ascending order from f₁ to f₅ and then returns tof₁, and subsequently shifts in ascending order again. Even when the lineA has such a shifting pattern, if the shifting direction of the line Bis opposite to the shifting direction of the line A, the sum of shiftvalues of the lines A and B can be equalized. That is, as illustrated inFIG. 8B, it is sufficient for the line B that the frequency first shiftsin descending order from f₅ to f₁ and then returns to f₅, andsubsequently shifts in descending order again.

The shifting pattern illustrated in FIG. 8A, if expressed by theshifting phase, is a shifting pattern repeating a cycle in which theshifting phase shifts in ascending order from 0° to 180° and thenreturns to 0°. The shifting pattern illustrated in FIG. 8B, if expressedby the shifting phase, is a shifting pattern repeating a cycle in whichthe shifting phase shifts in ascending order from 180° to 360° and thenreturns to 0°. Accordingly, when instructing a shift value correspondingto the phase angle of 180° for a power transmitter that has beeninstructed a shift value corresponding to the phase angle not less than0° and not greater than 180° as an initial value, the drive signalgenerator 14 instructs a shift value corresponding to the phase angle of0° in the next instruction. Further, when instructing a shift valuecorresponding to the phase angle of 360° for a power transmitter thathas been instructed a shift value corresponding to the phase angle notless than 180° and not greater than 360° as an initial value, the drivesignal generator 14 instructs a shift value corresponding to the phaseangle of 180° in the next instruction. Thereby, the shifting patterns inFIGS. 8A and 8B are obtained. Even in this case, it is preferred thatthe shifting phase difference be kept at the interval of 360/M°.

If preferred the frequency shifting directions of the line A and theline B are preferred to be the same for some reasons, the shift valuefrom which the frequency hopping starts may be made different asillustrated in FIG. 8C, so that the shifting phase difference can beheld even a little. According to the example illustrated in FIG. 8C, theshifting phase difference of 90° is held. Since the shifting phasedifference cannot be kept at 360/M°, the ripple becomes larger comparedto the case of holding the shifting phase difference at 360/M°. However,the effect of reducing the ripple can be expected than the case ofin-phase shifting.

(Second Example of the First Embodiment, in which the Frequency Relatedto the Peak of Amplitude Characteristics is Present in the Range ofShift Values)

FIGS. 9A to 9D are diagrams illustrating a second example of thepositional relationship between shift value range and amplitude ratio.In the second example, the frequency related to the peak of theamplitude ratio is present in the shift value range. FIG. 9A is adiagram illustrating amplitude characteristics in the second example.FIG. 9B is an enlarged view of FIG. 9A in a range where the frequencyshifting is performed. FIGS. 9C and 9D are diagrams illustrating theorder of shifting in the line A and the line B.

In the second example, when the shifting phase difference is kept at180° in the example case of two lines, it is feared that frequencies ofboth the line A and the line B may shift to the shift value where theamplitude ratio is maximized. Therefore, in the second example, theshifting phase difference is not kept at 360/M°.

The amplitude characteristics generally form a normal distribution.Therefore, when a medium value of the shift value is set to thefrequency related to the peak of the amplitude ratio, the frequencyshifts from the minimum shift value to the maximum shift value during a1/2 cycle. Therefore, when the shifting illustrated in FIGS. 5A and 5Boccurs in the line A and the line B, it is feared that both lines mayshift to the peak f₃ at the same time point.

Accordingly, in this case, it is preferred to hold the shifting phasedifference of 90° between the line A and the line B. As illustrated inFIGS. 9C and 9D, the shifting of the line A starts from f₁ in ascendingorder and the shifting of the line B starts from f₃ in ascending order.As illustrated in FIG. 6, when the shift value is f₁ and the shiftingstarts from this value in ascending order, the shifting phasecorresponding to the shift value f₁ is 0°. When the shift value is f₃and the shifting starts from this value in ascending order, the shiftingphase corresponding to the shift value f₃ is 90° because there are fiveshift values. Accordingly, the examples illustrated in FIGS. 9C and 9Dare shifting patterns in which the shifting phase difference is kept at90°.

In general, when the number of lines of the electric power transmissionsystem is “M”, it is preferred to hold the shifting phase differencebetween respective lines at 180/M°. That is, it can be said that thedifference between phase angles corresponding to any two of the shiftvalues of a plurality of power transmitters at the same time point ispreferably coincident substantially with any one of multiples from 1 toM−1 for 180/M. In other words, when “m” is defined as an integer equalto or greater than 1 and less than M, it is preferred that thedifference between the phase angles be expressed by 180(M−m)/M.

If the shifting phase difference cannot be kept at 180/M°, by settingthe maximum shifting phase difference between shift values instructed torespective lines as initial values to be less than 180°, two lines canbe prevented from shifting to the shift value of the peak at the sametime point. Therefore, the drive signal generator 14 may instructdifferent shift values whose corresponding phase angles are different by180° at most, as initial values, for respective power transmitters.Subsequently, the drive signal generator 14 may instruct shift valuesidentical to the shift values instructed last time or shift valuescorresponding to phase angles larger by one than the phase anglescorresponding to the shift values instructed last time.

FIGS. 10A and 10B are diagrams illustrating differences in amplituderatio when the shifting phase difference is kept at 180/M in the secondexample. FIG. 10A illustrates amplitude characteristics in the case oftwo lines. FIG. 10B illustrates amplitude characteristics in the case ofthree lines. Same as the first example illustrated in FIGS. 7A to 7C,regardless of the number of lines, the difference between the maximumamplitude ratio and the minimum amplitude ratio at the time of shiftingphase adjustment is smaller than the difference between the maximumamplitude ratio and the minimum amplitude ratio in the case of in-phase.Accordingly, even in the second example, it is understood that adjustingthe shifting phase can suppress the difference between the maximumamplitude ratio and the minimum amplitude ratio to be smaller than thecase of not adjusting the shifting phase.

Even in the second example, the order of shifting is not limited to thetriangular wave shifting. For example, as illustrated in FIG. 8C, thefrequency shifting direction may be set to either the ascending order orthe descending order in both the line A and the line B.

Although the interval of frequency shifting by the frequency hoppingvaries depending on the shifting number, the spread bandwidth and thelike, it is assumed that the frequency shifting is performed atintervals of approximately 50 μsec to 500 μsec. Therefore, in order toavoid any complicated control, it is preferred to calculate the settingvalues such as shift values, shifting timing, phase difference of drivesignals in advance. These setting values may be calculated each timewhile the frequency hopping is performed. In this case, writing from amain central processing unit (CPU) to a hardware register frequentlyoccurs at very short intervals for the processing capability of ageneric computer device incorporating the electric power transmissiondevice 1 according to the present embodiment. Changing the register eachtime during the frequency hopping is not preferred because it spendsmuch of the processing capability of the CPU and much of the writingband to the memory for the processing relating to the frequency hopping.

For example, it may be useful to use a memory table that stores valuessuch as shift values, length of period for sustaining the frequency,clock division ratio for changing the frequency, phase differencebetween drive signals for changing the frequency, and the like. Theorder of shifting the shift values may be implemented on the hardware.When setting values are written from the main CPU to the memory table,it is preferred to perform the writing in a state where the load of themain CPU is light, for example, before starting the power transmission.Thereby, in response to a signal instructing the frequency hopping fromthe main CPU, the hardware can automatically perform the frequencyhopping and conduction angle control processing.

Alternatively, aside from the main CPU, a, dedicated circuit for thefrequency hopping and the conduction angle control, e.g. a digitalsignal processor (DSP), is also provided in a power transmissioncircuit. In this manner, it is preferred to cause an arithmetic unitincluding a hardware device, a DSP, and a memory, which is independentfrom the main CPU, to perform the frequency hopping and the conductionangle control processing.

Next, the electric power reception device 2 will be described. Eachpower receptor of the electric power reception device 2 receiveselectric power through the magnetic field generated by a correspondingpower transmitter 13. In particular, mutual induction generateshigh-frequency current at the power reception coil unit 211 in the powerreceptor. Same as the power transmission coil unit 132, the coil type ofthe power reception coil unit 211 may be any type.

The rectifier 212 rectifies the high-frequency current supplied from thepower reception coil unit 211. For example, the rectifier 212 may beconfigured by a diode. DC currents outputting from respective rectifiers212 in respective lines are added by the adder 22 and the added currentis supplied to a power supply destination. It is assumed that the powersupply destination is a battery or any other electric device. The powersupply destination may be an internal device or an external device ofthe electric power reception device 2.

In the above description, it is assumed that the shifting phases are allshifted for respective lines. However, depending on the configuration,it may be unnecessary to shift the shifting phases of all lines. FIG. 11is a diagram illustrating a modified example of the first embodiment.Each line includes sub-lines. Two sub-lines A-1 and A-2 are provided inthe line A and two sub-lines B-1 and B-2 are provided in the line B,although the number of the sub-lines is not limited. Further, it isassumed that each sub-line includes constituent the same components asthose of the above-described lines, although not illustrated in thedrawings.

Each sub-line belonging to the same line shifts to the same frequency atthe same time point. That is, drive signals supplied to respectivesub-lines belonging to the same line are the same in frequency.Therefore, no ripple is suppressed with respect to the output current ofeach line. However, by combining it with output currents of other lines,the electric power reception device 2 can output a current suppressed inripple, in the same manner as above.

As mentioned above, in a case where a plurality of lines is divided intoa plurality of groups and where each of the groups and lines included inthe group regarded as line and sub-lines respectively, not all lines inthe electric power transmission system are different in shifting phase.

Further, an adder 213 for adding high-frequency currents from thesub-lines in each line is additionally provided in each line. Forexample, an adder 213A belonging to the line A adds currents of thesub-lines A-1 and A-2 and output the added current as a current of theline A. However, it is not always necessary to sum up the currents ofrespective sub-lines in each line. For example, the adder 22 may beconfigured to sum up all of the currents from respective sub-lines ofrespective lines.

As mentioned above, according to the first embodiment, the shiftingphase difference between respective lines can be adjusted whenperforming the frequency hopping. As a result, the total electric powerof the electric power reception device 2 can be suppressed fromfluctuating in amplitude. That is, ripple width can be suppressed.

Second Embodiment

FIG. 12 is a block diagram illustrating an exemplary electric powertransmission system according to a second embodiment. The electric powertransmission device 1 according to the second embodiment additionallyincludes a setting changer 15 (a shift value adjuster). Compared to thefirst embodiment, the second embodiment including the setting changer 15can perform electric power transmission with appropriate setting values.

The setting changer 15 confirms shift values registered beforehand forthe frequency hopping, and changes any setting value which may cause aproblem. In particular, the setting changer 15 performs the followingtwo changes.

(Deletion of a Combination of Shift Values of Respective Lines at EachTime Point)

When the shift values of the line A and the line B at the same timepoint are not sufficiently separated from each other, the frequencyhopping may not be effective as expected. The frequency hopping is forreducing the density of electromagnetic field intensity by spreading theleakage electromagnetic field energy on the frequency axis. However,when the shift values of the line A are close to the shift values of theline B, the electromagnetic field density in the frequency band aroundthese shift values is doubled and a strong leakage electromagnetic fieldis generated. In particular, when the difference in shift values of theline A and the line B is smaller than a resolution bandwidth (RBW) of ameasurement device that measures the leakage electromagnetic field, theintensity of the electromagnetic field by the line A and the intensityof the electromagnetic field by the line B are integrated and may beobserved as the intensity of a single electromagnetic field.Accordingly, in order to prevent the leakage electromagnetic fielddensity from increasing, it is preferred that the difference in shiftvalue between the lines A and B be equal to or greater than two timesthe RBW.

Therefore, in order to prevent the generation of a strong leakageelectromagnetic field, the setting changer 15 confirms the setting ofshift values and prevents any setting that may cause a problem frombeing used. In particular, the setting changer 15 determines whether thedifference in shift value between the lines A and B at the same timepoint is less than a predetermined threshold value. Then, if it isdetermined that the difference is less than the predetermined thresholdvalue, the setting changer 15 prohibits using the combination of theshift values of the lines A and B relating to this determination. Thepredetermined threshold value is, for example, two times the RBW.

FIG. 13 is a diagram illustrating processing relating to the deletion ofa combination from shift values of respective lines at each time point.The upper table of FIG. 13 illustrates exemplary setting of shift valuesof the lines A and B at each time point. When the difference between f₃and f₄ is less than the threshold value, the setting changer 15 removesthe combination of f₃ and f₄, and changes it to a combination scheduledat the next time point. The lower table of FIG. 13 illustrates exemplarysetting of shift values of the lines A and B after the change. Althoughthe upper table of FIG. 13 includes the combination of f₃ and f₄ asshift values at the third time point and the fourth time point, thelower table of FIG. 13 includes the combination of shift valuesinitially set for the fifth time point as the combination of shiftvalues at the third time point. Also, the lower table includes thecombination of shift values initially set for the sixth time point asthe combination of shift values at the fourth time point. In thismanner, before starting the frequency hopping, the setting changer 15can confirm the shifting pattern in advance and remove any setting thatmay cause a problem. As a result, the drive signal generator 14 canissue an instruction based on the changed setting table.

In the case of including three or more lines, if the difference in shiftvalue between any two of the shift values of a plurality of lines isless than the threshold value, using such a combination may beprohibited. Alternatively, considering only the physically neighboringlines, if the difference in shift value between the neighboring lines isequal to or greater than the threshold value, it may be determined thatthis combination is usable. Also, a flag for prohibiting the drivesignal generator 14 from using this combination may be given to thesetting table.

As mentioned above, the setting changer 15 may determine whether acombination of shift values scheduled to be instructed to a plurality ofpower transmitters is usable based on a difference between any two ofthe shift values belonging to this combination. The drive signalgenerator 14 may instruct shift values to each power transmitter basedon the combination of the shift values determined to be usable. Thereby,no leakage electromagnetic field is added between the lines, andgenerating a strong leakage electromagnetic field can be prevented.

(Determination of Shift Values to be Used in Each Line)

In the above-described embodiments, shift values to be used in each lineare the same although the shifting order of the shift values is changedin each line. Here, it is assumed that the setting changer 15 dividesthe shift values into some groups so that shift values to be used aredifferentiated for each line. For example, the setting changer 15determines that the line A uses shift values f₁ to f_(k) (k is aninteger greater than 1), the line B uses shift values f_(k+1) to f_(2k),and the line C uses shift values f_(2k+1) to f_(3k). In this manner,given shift values may be allocated to a group corresponding to eachline.

Differentiating the frequency band to be used in each line brings thatthe leakage electromagnetic field is not added between lines, and thenit can prevent a strong leakage electromagnetic field from beinggenerated. Even in this case, in order to reduce the ripple, it ispreferred to set the sum of shift values of respective lines as even aspossible at each time point.

FIGS. 14A and 14B are diagrams illustrating an exemplary shifting in thecase of differentiating shift values for each line. According to theexample illustrated in FIGS. 14A and 14B, the shift values to be usedare on the right side of the frequency related to the peak of theamplitude ratio (that is, when the minimum value of the shift value isgreater than the frequency related to the peak of the amplitude ratio).The shift value range may be on the left side of the peak of theamplitude ratio (that is, when the maximum value of the shift value issmaller than the frequency related to the peak of the amplitude ratio).

The shift values f₁ to f_(k) are allocated to the line A, and the shiftvalues f_(k+1) to f_(n) are allocated to the line B. In this case, thephase difference between the line A and the line B need not be adjusted.However, in the case where the allocated shifting number is the same,that is, when f_(n)=f_(2k), it is preferred that the difference betweenthe shifting phase by the shift values f₁ to f_(k) of the line A and theshifting phase by the shift values f_(k+1) to f_(n) of the line B bekept at 360/M, because the sum of the shift values is equalized betweenthe lines A and B. The shifting phase by the shift values f_(k+1) tof_(n) of the line B means that the shifting phase of f_(k+1) is 0° andthe shifting phase of f_(2k) is 180° when shifting in ascending orderand, after shifting to f_(k+1) in descending order, the shifting phaseof f_(k+1) is 360°.

FIGS. 15A and 15B are diagrams illustrating another exemplary shiftingin the case of differentiating shift values for each line. According tothe example illustrated in FIGS. 15A and 15B, the shift values to beused in two lines are present on both sides of the peak of the amplituderatio (according to this example, the maximum shift value of the line Ais smaller than the frequency related to the peak of the amplituderatio, and the minimum shift value of the line B is greater than thefrequency related to the peak of the amplitude ratio). Even in theexample illustrated in FIGS. 15A and 15B, the phase difference betweenthe line A and the line B need not be adjusted. However, in the casewhere the allocated shifting number is the same, it is preferred thatthe difference between the shifting phase by the shift values f₁ tof_(k) of the line A and the shifting phase by the shift values f_(k+1)to f_(n) of the line B be kept at 0°, because the sum of the shiftvalues is equalized between the line A and the line B.

As mentioned above, the setting changer 15 may divide a plurality ofshift values into at least two groups based on the magnitude of eachshift value and determine a corresponding group for each powertransmitter. Then, the drive signal generator 14 may instruct, to thepower transmitter 13, shift values belonging to the group correspondingto the power transmitter 13. Thereby, no leakage electromagnetic fieldis added between the lines, and it is possible to prevent a strongleakage electromagnetic field from being generated.

The processing of the setting changer 15 has only to be performed beforethe electric power transmission device 1 actually starts powertransmission. Both the deletion of combined shift values and thedetermination of shift values may be performed or only one of them maybe performed. In the case of performing both of them, there is noparticular limitation in the order. Further, the setting changer 15independently performs the processing of them. Therefore, description ofthe flow of this processing is omitted.

As mentioned above, according to the second embodiment, the settingchanger 15 adjusts the shift value to be used in each line. Thereby, inthe same manner as the other embodiment, the ripple can be reduced.Further, it is possible to avoid such a situation that a strong leakageelectromagnetic field is generated because the shift values are close toeach other at a certain time point.

Third Embodiment

In a third embodiment, exemplary arrangements of the power receptioncoil unit 211 in the case of using the electric power transmissionsystem according to the above-described embodiments will be illustrated.

FIG. 16 is a diagram illustrating an exemplary arrangement of the powerreception coil units 211. According to the example illustrated in FIG.16, the electric power transmission system is used for supply electricpower to a battery of an electric car or the like. The arrangement oftwo power reception coil units 211 for the lines A and B is illustrated.It is assumed that the power transmission coil units 132 are arranged atcorresponding positions on a ground surface, although not shown.

When performing electric power transmission with a plurality of lines,if mutual coupling occurs between different lines, for example, betweenthe power reception coil unit 211A of the line A and the power receptioncoil unit 211B of the line B, the electric power transmission efficiencydecreases. Therefore, according to the example illustrated in FIG. 16,in order to prevent the mutual coupling, the power reception coil units211 of the lines A and B are arranged apart from each other so as not tooccur the mutual coupling.

FIG. 17 is a diagram illustrating an exemplary arrangement of the powerreception coil units 211 that are the solenoid type. According to theexample illustrated in FIG. 17, it is assumed that each power receptioncoil unit 211 includes a coil of the solenoid type. The solenoid typecoil includes a core and a coil wound around the core (windings). Thesolenoid type coil generates a magnetic field in a directionperpendicular to a coil aperture surface (in the axial direction of thewindings). Hereinafter, a direction perpendicular to the coil aperturesurface is referred to as a direction of the solenoid type coil.

According to the example illustrated in FIG. 17, the magnetic field ofthe line A generates in the lateral direction (solid arrow direction) ona horizontal plane, and the magnetic field of the line B generates inthe vertical direction (dotted arrow direction). Therefore, since thegenerated magnetic fields are substantially orthogonal to each other, nomutual coupling occurs. Further, even in this arrangement, it ispossible to reduce the ripple by making the frequencies of the lines Aand B different. Arranging the directions of the solenoid type coils ofthe lines A and B so as to be substantially orthogonal to each other asmentioned above can prevent the mutual coupling from occurring betweenthe line A and the line B. Accordingly, it is possible to arrange thepower reception coil units 211 of the lines A and B close to each other.

FIG. 18 is a diagram illustrating an exemplary arrangement of the powerreception coil units 211 utilizing the reversed phase. The powerreception coil units 211 of the lines A and B are arranged within adistance where the mutual coupling may occur. Similarly, the powerreception coil units 211 of the lines C and D are arranged within adistance where the mutual coupling may occur. The lines A and B belongto a first group and the lines C and D belong to a second group.Further, the power reception coil units 211 of the first group and thepower reception coil units 211 of the second group are arranged apartfrom each other so as to keep a sufficient distance for preventing themutual coupling.

According to the example illustrated in FIG. 18, although the directionsof the solenoid type coils in respective groups are not substantiallyorthogonal and substantially parallel to each other, the mutual couplingbetween the coils can be suppressed to a required value or less becausethey are arranged obliquely. It is known that, the directions of themagnetic fields generated in respective lines in the same group arereversed and the leakage electromagnetic fields can be cancelled, whenhigh-frequency signals flowing in the power reception coil units 211 ofrespective groups are differentiated by 180° in phase of waveform(hereinafter, referred to as waveform phase), that is, when adjusted tobe in a reversed phase relationship. In order to utilize this fact,according to the example illustrated in FIG. 18, the lines A and Bbelonging to the first group are adjusted so as to be differentiated by180° in waveform phase. Similarly, the lines C and D belonging to thesecond group are adjusted so as to be differentiated by 180° in waveformphase. Thereby, it is possible to cancel the leakage electromagneticfields in the same group and reduce the leakage electromagnetic field.

In particular, the waveform phases of high-frequency signals of theinverters 131 of respective lines in the same group are set to beopposite in phase. Thereby, high-frequency signals flowing in the powerreception coil units 211 of respective lines become opposite in phase.In order to make the waveform phases of high-frequency signals of theinverter 131 opposite to each other, the drive signal generator 14 maycontinuously supply drive signals different by 180° in waveform phase tocorresponding two lines.

The coils in a reversed phase relationship need to be the same infrequency. Hence, it is impossible to make the frequencies of the linesbelonging to the same group different. According to the exampleillustrated in FIG. 18, the line A and the line B are the same infrequency, and the line C and the line D are the same in frequency.However, the frequencies of the first and second groups can be madedifferent because the distance between them is more than a distancewhere the mutual coupling can occur. Therefore, as the exampleillustrated in FIG. 11, the drive signal generator 14 instructs thelines belonging to the same group to shift to the same frequency at thesame time point and instructs the lines belonging to different groups toshift to different frequencies at the same time point. Thus, same as theexample illustrated in FIG. 11, the electric power reception device 2can output a current suppressed in ripple.

Since the same frequency is used within the same group and differentfrequencies are for different groups, a configuration similar to themodified example of the first embodiment illustrated in FIG. 11 may beused. In this case, the line A corresponds to the line A-1, the line Bcorresponds to the line A-2, the line C corresponds to the line B-1, andthe line D corresponds to the line B-2.

In the case of using the configuration of the modified example of thefirst embodiment, the drive signal generator 14 may output drive signalsfor the line A and drive signals for the line B that are different fromthe drive signals for the line A by 180° in the shifting phase, so thatthe drive signals are separated into drive signals different by 180° inwaveform phase in the line A and the line B. For example, a phaseinversion element may be used to invert the phase of one of two drivesignals separated. Thereby, the number of drive signals output from thedrive signal generator 14 can be reduced, and the processing and thecircuit configuration of the drive signal generator 14 can besimplified.

FIG. 19 is a diagram illustrating an exemplary arrangement of the powerreception coil units 211 utilizing the reversed phase when the powerreception coil units 211 use coils of the solenoid type. There are twocombinations of the power reception coil units 211 that are the same inthe direction of the solenoid type coils. The solenoid type coils ofeach combination are arranged so that the directions thereof aresubstantially orthogonal to each other. Further, solenoid type coils ofthe same combination are arranged to be substantially parallel to eachother although they are not on the same straight line. In addition, allthe solenoid type coils are arranged so as not to overlap with eachother in plan view. Here, a combination to which the line A and the lineB (or the line A-1 and the line A-2) arranged substantially parallel toeach other belong is referred to as a first group. A combination towhich the line C and the line D (or the line B-1 and the line B-2)arranged substantially parallel to each other is referred to as a secondgroup. Even in the example illustrated in FIG. 19, the configuration ofthe modified example of the first embodiment may be used.

Same as the example illustrated in FIG. 18, the power reception coilunits 211 belonging to each group cancel their leakage electromagneticfields by reversing in phase the drive signals for the correspondinginverters 131. That is, the line A and the line B (or the line A-1 andthe line A-2) belonging to the first group are adjusted to be differentby 180° in waveform phase. In addition, the line C and the line D (orthe line B-1 and the line B-2) belonging to the second group areadjusted to be different by 180° in waveform phase. Further, since thecoils belonging to different groups are substantially orthogonal to eachother in solenoid type coil direction, no mutual coupling occurs betweenrespective groups, same as the example illustrated in FIG. 17. Hence, itis possible to make the frequency different between the first group andthe second group. Therefore, the drive signal generator 14 instructsdifferent shift values for the first group and the second group, therebyreducing the ripple of the output current of the electric powerreception device 2 and realizing the arrangement illustrated in FIG. 19in which four power reception coil units 211 can positioned closely. Itis also possible to additionally arrange power reception coil units 211in distant positions where no mutual coupling with the four powerreception coil units 211 occurs.

As mentioned above, by using the drive signals and the arrangement ofthe power reception coil units 211 for canceling leakage electromagneticfields, two or more power reception coil units 211 can be arrangedclosely. As a result, in a system using the electric power transmissionsystem, for example, in a system for charging batteries of an electricvehicle, the problem of space can be solved and the amount oftransmittable electric power can be increased.

The controls in the embodiments described above may be performed only ina specific period, such as a period in which reducing the ripple isrequired. In this case, shifting to an arbitrary frequency is notrestricted in a period in which no control is performed. In addition,the above-described controls may be performed only for a specific lineand it is not always necessary to perform the controls for all lines.

Although it is assumed that a dedicated circuit realizes each processingin the present embodiment, a program stored in a memory of the CPU mayrealize processing relating to circuit control, such as instruction oftiming for changing the frequency.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and, their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. An electric power transmission device that periodically shifts afrequency of a magnetic field to a plurality of predetermined shiftvalues and that transmits electric power by utilizing the magneticfield, the electric power transmission device comprising: a plurality ofpower transmitters configured to each generate a magnetic field; and aninstructor configured to output an instruction signal indicating a shiftvalue to be shifted to each of the power transmitters to instruct theshift value to be shifted to each of the power transmitters, wherein theinstructor instructs the shift value to be shifted in such a manner thatat least a part of the magnetic fields of the plurality of powertransmitters are different in frequency at the same time point.
 2. Theelectric power transmission device according to claim 1, wherein each ofthe power transmitters includes: an inverter configured to generatehigh-frequency current from DC current; and a power transmission coilconfigured to generate the magnetic field when the high-frequencycurrent flows, wherein the instruction signal is a drive signal for theinverter, and the frequency of the high-frequency current shifts to theinstructed shift value as the frequency of the instruction signalchanges to a value corresponding to the instructed shift value.
 3. Theelectric power transmission device according to claim 1, wherein in thecase of expressing each shift value and shifting direction by phaseangle when one cycle of periodic shifting including an ascending shiftfrom a minimum value of the plurality of shift values to a maximum valueand a descending shift from the maximum value to the minimum value isregarded as 360°, when the frequency related to a peak of amplitudecharacteristics of the magnetic field is not present between the minimumvalue and the maximum value, the instructor instructs different shiftvalues as initial values to respective power transmitters and, afterinstructing the initial values, the instructor instructs a shift valueidentical to that instructed last time or a shift value corresponding toa phase angle that is larger by one than the phase angle correspondingto the shift value instructed last time to each power transmitter. 4.The electric power transmission device according to claim 3, whereinwhen instructing a shift value corresponding to a phase angle of 180° toa power transmitter that has been instructed a shift value correspondingto a phase angle equal to or greater than 0° and less than 180° as aninitial value, the instructor instructs a shift value corresponding tothe phase angle of 0° in the next instruction, and when instructing ashift value corresponding to a phase angle of 360° to a powertransmitter that has been instructed a shift value corresponding to aphase angle equal to or greater than 180° and less than 360° as aninitial value, the instructor instructs a shift value corresponding tothe phase angle of 180° in the next instruction.
 5. The electric powertransmission device according to claim 3, wherein the number of theplurality of power transmitters is M (M is an integer equal to orgreater than 2), and the difference between phase angles correspondingto any two of shift values of the plurality of power transmitters at thesame time point is substantially coincident with any one of multiplesfrom 1 to M−1 for 360/M.
 6. The electric power transmission deviceaccording to claim 1, wherein in the case of expressing each shift valueby phase angle when one cycle of periodic shifting including anascending shift from a minimum value of the plurality of shift values toa maximum value and a descending shift from the maximum value to theminimum value is regarded as 360°, when the frequency related to a peakof amplitude characteristics of the magnetic field is present betweenthe minimum value and the maximum value, the instructor instructsdifferent shift values whose corresponding phase angles are different by180° at most as initial values to respective power transmitters, andafter instructing the initial values, the instructor instructs a shiftvalue identical to that instructed last time or a shift valuecorresponding to a phase angle that is larger by one than the phaseangle corresponding to the shift value instructed last time to eachpower transmitter.
 7. The electric power transmission device accordingto claim 4, wherein the number of the plurality of power transmitters isM (M is an integer equal to or greater than 2), and the differencebetween phase angles corresponding to any two of the shift values of theplurality of power transmitters at the same time point is substantiallycoincident with any one of multiples from 1 to M−1 for 180/M.
 8. Theelectric power transmission device according to claim 1, furthercomprising a shift value adjuster configured to determine whether acombination of shift values scheduled to be instructed to respectivepower transmitters is usable based on a difference between any two ofshift values belonging to the combination, wherein the instructorinstructs shift values to respective power transmitters based on thecombination of shift values determined to be usable.
 9. The electricpower transmission device according to claim 1, further comprising ashift value adjuster configured to divide the plurality of shift valuesinto at least two groups based on the magnitude thereof and determine agroup corresponding to respective power transmitters, wherein theinstructor instructs, to a power transmitter, shift values belonging toa group corresponding to the power transmitter.
 10. An electric powertransmission system that sequentially shifts a frequency of a magneticfield to a plurality of shift values and transmits electric power byutilizing the magnetic field, the system comprising: an electric powertransmission device; and an electric power reception device, wherein theelectric power transmission device includes: a plurality of powertransmitters configured to each generate a magnetic field; and aninstructor configured to output an instruction signal indicating a shiftvalue to be shifted to each of the power transmitters to instruct theshift value to be shifted to each of the power transmitters, theelectric power reception device includes: a plurality of power receptioncoils configured to each generate high-frequency current by the magneticfield of a corresponding power transmitter; and an adder configured toadd the high-frequency currents from the plurality of power receptioncoils, and the instructor instructs the shift values to be shifted insuch a manner that at least a part of the magnetic fields of theplurality of power transmitters are different in frequency at the sametime point.
 11. The electric power transmission system according toclaim 10, wherein the plurality of power reception coils includes firstand second power reception coils that are arranged in such a manner thatdirections of magnetic fields received by the first and second powerreception coils are substantially orthogonal to each other in plan view,and the instructor instructs the shift values in such a manner that themagnetic fields of power transmitters corresponding to the first andsecond power reception coils are different in frequency.
 12. Theelectric power transmission system according to claim 10, wherein theelectric power transmission device includes at least first to fourthpower transmitters, the electric power reception device includes atleast first to fourth power reception coils corresponding to the firstto fourth power transmitters, the first and second power reception coilsare arranged in such a manner that directions of magnetic fieldsreceived by the first and second power reception coils are substantiallyparallel to each other in plan view, the third and fourth powerreception coils are arranged in such a manner that directions ofmagnetic fields received by the third and fourth power reception coilsare substantially parallel to each other in plan view, a combination ofthe first and second power reception coils and a combination of thethird and fourth power reception coils are arranged apart from eachother so as to keep a distance for preventing mutual coupling fromoccurring, magnetic fields generated by the first and second powertransmitters are in a reversed phase relationship, magnetic fieldsgenerated by the third and fourth power transmitters are in a reversedphase relationship, and the instructor instructs the same shift valuesto the first and second power transmitters, while instructing, for thethird and fourth power transmitters, the same shift values that aredifferent from the shift values instructed to the first and second powertransmitters.
 13. The electric power transmission system according toclaim 10, wherein the electric power transmission device includes atleast first to fourth power transmitters, the electric power receptiondevice includes at least first to fourth power reception coilscorresponding to the first to fourth power transmitters, the first tofourth power reception coils are arranged in such a manner that:directions of magnetic fields received by the first and second powerreception coils are substantially parallel to each other in plan view;directions of magnetic fields received by the third and fourth powerreception coils are substantially parallel to each other in plan view;and the directions of the magnetic fields received by the first andsecond power reception coils are substantially orthogonal to thedirections of the magnetic fields received by the third and fourth powerreception coils in plan view, magnetic fields generated by the first andsecond power transmitters are in a reversed phase relationship, magneticfields generated by the third and fourth power transmitters are in areversed phase relationship, and the instructor instructs the same shiftvalues to the first and second power transmitters, while instructing,for the third and fourth power transmitters, the same shift values thatare different from the shift values instructed to the first and secondpower transmitters.